Re-examination of the Cycloaddition of Cycloheptatriene with Maleic Anhydride

Cycloaddition of cycloheptatriene to maleic anhydride was re-examined and found to produce, in addition to the reported main product anti-tricyclo[3.2.2.02,4]non-6-endo-8,endo-9-dicarboxylic anhydride (1), the exo, exo isomer of this compound (4) and bicyclo[3.2.2]nona-2,6-diene-endo-8,endo-9-dicarboxylic anhydride (5). Evidence for these structures involving the orientation of the cyclopropane ring in 1 and 4 and the configuration of the carboxylic anhydride was provided by PMR spectroscopy using the intramolecular nuclear Overhauser effect and paramagnetic induced shift due to tris(dipivalomethanato)europium(III). The structure assignment by Alder and Jacobs for 1 was found to be correct, but not the one by Schenk et al The difference in free energies of activation leading to 1 and 4 was determined.